All WordPress themes like Twenty Seventeen, Twenty Sixteen and Twenty Fifteen have a footer message “Proudly powered by WordPress” displayed at the bottom of the site. This free footer message is an easy identification for hackers to find a WordPress site using default themes.
Proudly Powered By WordPress Footer
By default WordPress does not allow to remove this footer message. But you have the following two methods to hide or remove it from your site.
YouTube video: How to Install WordPress theme